Effect of partial genetic resistance on efficacy of Topsin fungicide for control of white mold disease in pinto bean

Authors: Miklas, Phillip - Phil; Porter, Lyndon

Submitted to: ARS Sclerotinia Initiative Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 1/21/2008
Publication Date: 1/23/2008
Citation: Miklas, P. N., and L. Porter. 2008. Effect of partial genetic resistance on efficacy of Topsin fungicide for control of white mold disease in pinto bean. National Sclerotinia Initiative 6th Annual Meeting, Jan. 23-25, 2008. p. 21.

Interpretive Summary:

Technical Abstract: Pinto bean is the most important dry bean market class grown in the U.S., but is one of the most susceptible to white mold disease. Developing pinto bean with partial resistance is a major goal of plant breeders, but the effect of partial resistance on efficacy of fungicide application for disease management is unknown. Our goal was to document the effect partially resistant or less susceptible lines and cultivars have on overall white mold disease control in pinto bean. The pinto breeding line USPT-WM-1 with partial resistance, less susceptible pinto cultivars Maverick and Winchester, upright pinto cultivar Aztec with potential disease avoidance, and Montrose pinto as a susceptible check, were selected for use in this study. The select pintos were grown in replicated trials in multiple environments under moderate to severe disease pressure. A commercial fungicide Topsin M was applied at recommended rates and bloom stages. Four spray treatments were used, 0, 1, 2, and 3, applications. Across years and genotypes Topsin M reduced disease severity by 32, 37, and 53%, for 1, 2, and 3 applications, respectively, but only had a positive yield response for 1 (14%) and 2 applications (23%), suggesting that a third application is unnecessary and two applications is economically superior to one. Two Topsin M applications improved yield the most (26%) for the four most susceptible pintos and benefited yield (4%) of the partially resistant cultivar USPT-WM-1 the least because this line has stable yield potential under moderate to severe disease pressure regardless of fungicide application. It was observed that reduced lodging, increased plant height, and late maturity were moderately correlated (~45%) with reduced disease severity, indicating importance of disease avoidance traits in combating white mold disease. Aztec with disease avoidance traits alone was highly susceptible in the absence of a fungicide application. USPT-WM-1 has disease avoidance traits too but the avoidance is augmented by physiological resistance which is lacking in Aztec. In summary results suggest that pinto cultivars with combination of partial resistance and disease avoidance traits will yield effectively under moderate white mold disease pressure without Topsin M fungicide.